This invention relates to a tape automated bonding film (will be abbreviated to a TAB film hereinafter) for use in mounting a chip.
Various kinds of packaging technology to package a chip have been proposed. Among others, TCP (tape-carrier package) technology which packages a chip mounted on a TAB film is superior to the other technology in view of making thin packages. Owing to this property of the TCP, packages which are manufactured by the use of TCP technology are very often utilized in a wide variety of devices, for instance, note type PCs (personal computers).
More specifically, a peripheral TAB film is often used as a TAB film in the TCP technology and, therefore, the TCP technology using the peripheral TAB film may be also called a peripheral TAB technology. In the peripheral TCP technology, the peripheral TAB film has a base film divided into a chip mounting area for a chip and an outside area for surrounding the chip mounting area. In particular, the chip mounting area is further sub-divided into a central region and a peripheral region located outside of the central region.
It is to be noted that the peripheral TAB film has a plurality of connection points formed on the peripheral region and a plurality of inner leads (or inner lead lines) which are formed on the base film and are connected to the connection points. Herein, the inner leads are radially laid toward the outside region from the connection points while the remaining edges of the inner leads are connected to bumps for terminals of printed circuit or outer leads.
Under the circumstances, a chip is mounted on the peripheral TAB film with electrode pads (merely may be called pads hereinafter) of the chip connected to the connection points. As readily understood from the above, the electrode pads of the chip for the peripheral TAB film are arranged only on a peripheral part of the chip surface.
However, the peripheral TAB technology has shortcomings as will be described when a density of integrated circuits in chips becomes high with progress of the semiconductor technology.
Generally, it is required that high density chips have a great number of electrode pads. Taking this into consideration, intervals or pitches between the electrode pads must become narrow in order to prevent the package from being large in size when such high density chips are manufactured by the peripheral TAB technology. However, narrowing pitches between electrode pads is restricted by a package process and a board assembling process. Alternatively, it is assumed that various sizes of packages all have same pitches between pads. In this event, the packages inevitably become large in size with an increase of electrode pads.
On the other hand, it is a recent trend that requirements have been directed to packages which are small in size and thin in thickness because an electronic apparatus formed by a plurality of such packages becomes small and thin. As described before, the peripheral TAB technology cannot meet these requirements.
To respond to the requirements, an area TAB technology has been proposed. The area TAB technology differs from the peripheral TAB technology and, in the area TAB technology, pads are arranged not only on a peripheral region of the chips surface but also on other region, such as a region located inside of the peripheral region. For the purpose of this, the area TAB technology uses, instead of the above mentioned peripheral TAB film, an area TAB film which further has other connection points corresponding to the pads located on such other region. Needless to say, the other connection points are also connected to other lead lines.
According to the technology, many pins can be derived from many electrode pads without an increase of a package size and with pitches between pads kept unchanged.
At any rate, when intervals between inner leads become narrow, all the conventional technologies reach the limits of manufacturing a TAB film itself. This is due to necessity of a process margin on designing packages which have an increased number of pads. Such limits also result from a reduction of degrees of freedom regarding leads each of these conventional technologies. Attempts to forcibly exceed the limit give rise to breakage or short circuits in lead patterns and bring about decrease of yield.
For avoiding the problems of these techniques, further proposal has been made about TAB films which use a multi-layered metal wiring technique. Such a TAB film may have, for example, two metal wiring layers.
However, such a type of a TAB film comprising two metal wiring layers further requires a process of adding a metal layer to the film and another process of forming via holes into the film owing to its structure. Moreover, via holes must be minimized in order to make a package small in size. Thus, the use of such multi-layered metal wiring technique indispensably makes a manufacturing cost high and, therefore, is undesirable in the consumer market.